In the past, a polyamide resin that is capable of being molded into a prescribed shape by heat-melting has been used as a material for molding an electronic part. Generally, as a polyamide, 6-nylon, 66-nylon, and the like have been widely used. However, such an aliphatic polyamide lacks sufficient heat resistance as a raw material for producing a surface mount part such as a connector that is exposed to high temperature like a reflow soldering process, although it is excellent in moldability. With such a background, 46-nylon has been developed as a polyamide having high heat resistance, but it has a problem of high water absorption. For this reason, an electric and electronic part molded by using 46-nylon resin composition may sometimes change in size by water absorption, thereby causing such a problem as blistering, so-called bulging, during heating in a reflow soldering process when a molded article contains absorbed water. Particularly, in recent years the surface mounting method is being shifted to the use of a lead-free solder in view of an environmental concern. A lead-free solder has higher melting point as compared with a conventional lead solder, inevitably increasing a mounting temperature by 10 to 20° C., and thus the use of 46-nylon is becoming difficult.
As a countermeasure, an aromatic polyamide derived from an aromatic dicarboxylic acid such as terephthalic acid and an aliphatic alkylene diamine has been developed. An aromatic polyamide has further excellent properties in heat resistance and low water absorption as compared with an aliphatic polyamide such as 46-nylon. However, it has a problem of lacking toughness though it is possible to improve rigidity as compared with 46-nylon. Especially, in the use of a thin fine-pitch connector, if a connector material is poor in toughness, such phenomena as cracking and whitening occur during pushing in and pulling off of a terminal, and thus it has been desired to develop a material having high toughness.
For the above-mentioned problems, it is possible to improve toughness by increasing the content of a polyamide resin and decreasing the amount of a flame retardant. However, in the use of an electronic part such as a connector, high flame and fire retardancy, such as V-0 rating, which is generally stipulated in the Underwriters Laboratories standard UL-94 is often requested, but it has been difficult to attain good toughness without impairing incombustibility.
In order to increase toughness by improving compatibility between a polyamide resin and a flame retardant, there is a publicly known technology to use a brominated polyphenylene ether or a poly(brominated styrene) containing an epoxy group in the molecule as a flame retardant. However, in the case of a resin such as an aromatic polyamide resin that is molded at high temperature, there have been the cases where its use was restricted because such phenomena as decomposition of a molding material, variance and decrease of product mechanical properties, and formation of a discolored material occurred due to insufficient heat stability during molding.
In Patent Document 1, a flame retardant polyamide resin composition comprising an aromatic polyamide and a brominated polystyrene having low viscosity is disclosed. However, there is a problem that sufficient toughness and heat resistance are not attained. Also, in Patent Document 2, a flame retardant resin composition comprising an aliphatic polyamide and a brominated polystyrene having a specific molecular weight is disclosed, but it has a problem in heat resistance and flowability. Further, in Patent Document 3, a flame retardant polyamide resin composition using poly(brominated styrene) as a flame retardant is disclosed, but it has a problem that sufficient heat resistance is not attained.
In addition to the above-mentioned problems, in a flame retardant composition using an aromatic polyamide resin having melting point of 300° C. or above, the molding temperature is so high that discoloration of a molding material or a molded article due to partial elimination of bromine group contained in the flame retardant and corrosion of a mold due to generation of bromine gas can take place easily, and thus development of a material having good moldability is desired.
Further, in Patent Documents 4 and 5, a technology relating to a flame retardant composition comprising nylon-4,6, and as a flame retardant, a halogenated aromatic compound and a hydrotalcite compound are disclosed, but the composition lacks sufficient heat stability during molding under the conditions of high temperature and long duration. In addition, it is inferior in heat resistance, or blister resistance, in a reflow soldering process using a lead-free solder.
In Patent Document 6, a flame retardant composition comprising an aromatic polyamide resin, and as a flame retardant, a terminal-modified poly(bromophenylene oxide) and a hydrotalcite compound whose crystal water is removed by 30% or more is disclosed. But, in the flame retardant composition, it also lacks sufficient heat stability during molding under the conditions of high temperature and long duration.    Patent Document 1: Japanese Patent Laid-Open Publication No. H6-263985    Patent Document 2: Japanese Patent Laid-Open Publication No. H9-227625    Patent Document 3: Japanese Patent Laid-Open Publication No. H5-194842    Patent Document 4: Japanese Patent Laid-Open Publication No. S63-223060    Patent Document 5: Japanese Patent Laid-Open Publication No. H6-345963    Patent Document 6: Japanese Patent Laid-Open Publication No. 2001-31863